baht_text.php

<?php
const BAHT_TEXT_NUMBERS = array('ศูนย์', 'หนึ่ง', 'สอง', 'สาม', 'สี่', 'ห้า', 'หก', 'เจ็ด', 'แปด', 'เก้า');
const BAHT_TEXT_UNITS = array('', 'สิบ', 'ร้อย', 'พัน', 'หมื่น', 'แสน', 'ล้าน');
const BAHT_TEXT_ONE_IN_TENTH = 'เอ็ด';
const BAHT_TEXT_TWENTY = 'ยี่';
const BAHT_TEXT_INTEGER = 'ถ้วน';
const BAHT_TEXT_BAHT = 'บาท';
const BAHT_TEXT_SATANG = 'สตางค์';
const BAHT_TEXT_POINT = 'จุด';

/**
 * Convert baht number to Thai text
 * @param double|int $number
 * @param bool $include_unit
 * @param bool $display_zero
 * @return string|null
 */
function baht_text ($number, $include_unit = true, $display_zero = true)
{
    if (!is_numeric($number)) {
        return null;
    }

    $log = floor(log($number, 10));
    if ($log > 5) {
        $millions = floor($log / 6);
        $million_value = pow(1000000, $millions);
        $normalised_million = floor($number / $million_value);
        $rest = $number - ($normalised_million * $million_value);
        $millions_text = '';
        for ($i = 0; $i < $millions; $i++) {
            $millions_text .= BAHT_TEXT_UNITS[6];
        }
        return baht_text($normalised_million, false) . $millions_text . baht_text($rest, true, false);
    }

    $number_str = (string)floor($number);
    $text = '';
    $unit = 0;

    if ($display_zero && $number_str == '0') {
        $text = BAHT_TEXT_NUMBERS[0];
    } else for ($i = strlen($number_str) - 1; $i > -1; $i--) {
        $current_number = (int)$number_str[$i];

        $unit_text = '';
        if ($unit == 0 && $i > 0) {
            $previous_number = isset($number_str[$i - 1]) ? (int)$number_str[$i - 1] : 0;
            if ($current_number == 1 && $previous_number > 0) {
                $unit_text .= BAHT_TEXT_ONE_IN_TENTH;
            } else if ($current_number > 0) {
                $unit_text .= BAHT_TEXT_NUMBERS[$current_number];
            }
        } else if ($unit == 1 && $current_number == 2) {
            $unit_text .= BAHT_TEXT_TWENTY;
        } else if ($current_number > 0 && ($unit != 1 || $current_number != 1)) {
            $unit_text .= BAHT_TEXT_NUMBERS[$current_number];
        }

        if ($current_number > 0) {
            $unit_text .= BAHT_TEXT_UNITS[$unit];
        }

        $text = $unit_text . $text;
        $unit++;
    }

    if ($include_unit) {
        $text .= BAHT_TEXT_BAHT;

        $satang = explode('.', number_format($number, 2, '.', ''))[1];
        $text .= $satang == 0
            ? BAHT_TEXT_INTEGER
            : baht_text($satang, false) . BAHT_TEXT_SATANG;
    } else {
        $exploded = explode('.', $number);
        if (isset($exploded[1])) {
            $text .= BAHT_TEXT_POINT;
            $decimal = (string)$exploded[1];
            for ($i = 0; $i < strlen($decimal); $i++) {
                $text .= BAHT_TEXT_NUMBERS[$decimal[$i]];
            }
        }
    }

    return $text;
}